Book cover for Molecular Cell Biology

Molecular Cell Biology

Harvey Lodish, Arnold Berk, Chris A. Kaiser

ISBN #9781464183393

8th Edition

406 Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This section of the textbook covers the fundamental principles of biochemical energetics, including the concepts of free energy (?G), equilibrium constants (Keq), and activation energy. It explains the difference between exergonic and endergonic reactions and how cells couple unfavorable reactions with favorable ones, primarily through ATP hydrolysis. The text also addresses the importance of redox reactions and the role of electron carriers, as well as how buffers help maintain the precise pH required for optimal cellular function. Understanding these principles is essential for analyzing how cells harness, convert, and utilize energy in various biochemical processes.

Learning Objectives

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Key Concepts

CONCEPT

DEFINITION

Biomembrane Structure

The organized, selectively permeable barrier of the cell composed primarily of amphipathic phospholipids, cholesterol, and proteins, which self?assembles into a lipid bilayer. These structures regulate membrane fluidity, thickness, and the assembly and function of integral and peripheral membrane proteins.

Example Problems

Example 1

The gecko is a reptile with an amazing ability to climb smooth surfaces, including glass. Geckos appear to stick to smooth surfaces via van der Waals interactions between septa on their feet and the smooth surface. How is this method of stickiness advantageous over covalent interactions? Given that van der Waals forces are among the weakest molecular interactions, how can the gecko's feet stick so effectively?

Example 2

The $\mathrm{K}^{+}$ channel is an example of a transmembrane protein (a protein that spans the phospholipid bilayer of the plasma membrane). What types of amino acids are likely to be found (a) lining the channel through which $\mathrm{K}^{+}$ passes, $(\mathrm{b})$ in contact with the hydrophobic core of the phospholipid bilayer containing fatty acyl groups, (c) in the cytosolic domain of the protein, and (d) in the extracellular domain of the protein?

Example 3

V-M-Y-F-E-N: This is the single-letter amino acid abbreviation for a peptide. What is the net charge of this peptide at pH $7.0 ?$ An enzyme called a protein tyrosine kinase can attach phosphates to the hydroxyl groups of tyrosine (Y). What is the net charge of the peptide at $\mathrm{pH} 7.0$ after it has been phosphorylated by a tyrosine kinase? What is the likely source of phosphate used by the kinase for this reaction?

Example 4

Disulfide bonds help to stabilize the three-dimensional structure of proteins. What amino acids are involved in the formation of disulfide bonds? Does the formation of a disulfide bond increase or decrease entropy $(\Delta S)$ ?

Example 5

In the 1960 s, the drug thalidomide was prescribed to pregnant women to treat morning sickness. However, thalidomide caused severe limb defects in the children of some women who took the drug, and its use for morning sickness was discontinued. It is now known that thalidomide was administered as a mixture of two stereoisomeric compounds, one of which relieved morning sickness and the other of which was responsible for the birth defects. What are stereoisomers? Why might two such closely related compounds have such different physiological effects?
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